An epitaxial wafer including a silicon water obtained by cutting a silicon monocrystal and an epitaxial film grown through vapor-phase growth on the surface of the silicon wafer has been known. The epitaxial film is formed through CVD (a kind of vapor-phase growth). There is theoretically no oxygen in the epitaxial film and an oxygen concentration in the epitaxial film is actually zero or almost zero. When the oxygen concentration in the epitaxial film is low as described above, for instance, during a heat treatment (e.g. a device process), a dislocation sometimes occurs in the epitaxial film and the dislocation sometimes extends. Thus, studies have been made in order to avoid the occurrence of such dislocation extension (see, for instance, Patent Literature 1).
In Patent Literature 1, it is disclosed that the oxygen concentration on the surface of the epitaxial film relates to the occurrence of the dislocation and the extension of the dislocation can be prevented by setting the oxygen concentration on the surface of the epitaxial film within a range from 1.0×1017 to 12×1017 atoms/cm3 (according to ASTM F-121, 1979). Patent Literature 1 also discloses that, in order to manufacture an epitaxial silicon wafer having such a property, an oxygen-concentration-setting heat-treatment step, in which the silicon wafer is subjected to a heat treatment at a heat treatment temperature in a range from 900 degrees C. to the melting point of silicon, is performed after forming the epitaxial film. The high-temperature heat treatment applied after forming the epitaxial film thermally diffuses the oxygen solid-solved in the silicon wafer to the epitaxial film to increase the oxygen concentration in the epitaxial film.